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https://github.com/cookiengineer/audacity
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94 lines
2.6 KiB
Common Lisp
94 lines
2.6 KiB
Common Lisp
;nyquist plug-in
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;version 3
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;type process
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;categories "http://lv2plug.in/ns/lv2core#LowpassPlugin"
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;name "Low Pass Filter..."
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;action "Performing Low Pass Filter..."
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;info "by Dominic Mazzoni, modified by David R. Sky\nReleased under terms of the GNU General Public License Version 2\nAttenuates high frequencies above your specified cutoff frequency.\nHigher rolloff values give a sharper attenuation of frequencies above\nthe cutoff frequency. If using a rolloff of 12 dB, a [q] value greater than\ndefault 0.7 increases resonance ['ringing'] of the cutoff frequency and\ncould result in clipping.""
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;control rolloff-choice " Rolloff [dB per octave]" choice " 6 dB,12 dB,24 dB,36 dB,48 dB" 0
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;control q " Filter quality [q] for 12 dB rolloff" real "" 0.7071 .1 20
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;control f " Cutoff frequency [Hz]" real "" 1000 1 20000
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; note that all Nyquist lowpass functions
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; [lp, lowpass2, lowpass4, lowpass6, lowpass8]
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; are defined below with -s suffix.
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; This enables lowpass functions other than lp
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; to deal with stereo selection,
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; and dummy q arg for all but lowpass2
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; 6dB/octave
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(defun lp-s (s f q) ; dummy q arg
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(lp s f))
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; 12dB/octave
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(defun lowpass2-s (s f q)
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(if (arrayp s)
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(vector (lowpass2 (aref s 0) f q)
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(lowpass2 (aref s 1) f q))
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(lowpass2 s f q)))
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; 24dB/octave
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(defun lowpass4-s (s f q) ; dummy q arg
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(if (arrayp s)
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(vector (lowpass4 (aref s 0) f)
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(lowpass4 (aref s 1) f))
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(lowpass4 s f)))
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; 36dB/octave
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(defun lowpass6-s (s f q) ; dummy q arg
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(if (arrayp s)
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(vector (lowpass6 (aref s 0) f)
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(lowpass6 (aref s 1) f))
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(lowpass6 s f)))
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; 48dB/octave
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(defun lowpass8-s (s f q) ; dummy q arg
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(if (arrayp s)
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(vector (lowpass8 (aref s 0) f)
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(lowpass8 (aref s 1) f))
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(lowpass8 s f)))
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; check function: returns 1 on error
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(defun check (arg min max)
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(if (and (>= arg min) (<= arg max))
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0 1))
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; initialize blank error-msg
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(setf error-msg "")
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; check for erroneous q value
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(setf error-msg (if
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(and (= rolloff-choice 1)
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(= (check q 0.1 20) 1))
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(strcat error-msg (format nil
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"q value ~a lies outside valid range 0.1 to 20
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for your chosen rolloff of 12 dB per octave.
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" q))
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error-msg))
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; check for erroneous frequency cutoff value
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(setf error-msg (if
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(= (check f 1 20000) 0)
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error-msg
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(strcat error-msg (format nil
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"Cutoff frequency ~a Hz lies outside valid range 1 to 20000.
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" f))))
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(cond
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((> (length error-msg) 0)
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(setf error-msg (strcat (format nil
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"Error - \n\nYou have entered at least one invalid value:
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") error-msg))
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(format nil "~a" error-msg))
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;
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(t ; perform lowpass effect
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(funcall (nth rolloff-choice '(lp-s lowpass2-s lowpass4-s lowpass6-s lowpass8-s))
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s f q)))
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; from previous commit
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; arch-tag: c2d96e46-b4e2-47c0-9a19-761011418e02
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